Switching Transducer Driver Circuitry

The present disclosure relates to switching transducer driver circuitry. In particular, the present disclosure relates to a switching output stage for class D amplifier circuitry.

Switching transducer drivers such as Class D amplifiers are increasingly being used in electronic devices for which power efficiency is important, such as mobile telephones, portable media players, laptop and tablet computers, wireless headphones, earphones and earbuds. Such transducer drivers are also increasingly finding use in automotive applications, e.g. in vehicle audio systems and the like.

A typical switching transducer driver (e.g. a Class D amplifier) includes a modulator stage and an output stage. In low-power applications such as portable audio devices it is common for the output stage to be implemented as a full-bridge output stage, with a load such as a speaker being coupled in a bridge-tied load configuration between first and second half-bridges, each of which comprises a first and second series-connected switches such as MOSFETs.

1 FIG. 100 110 120 130 112 122 110 120 is a simplified schematic representation of a full bridge output stagecomprising a first half-bridgeand a second half-bridge, which together provide a differential output voltage VOut for driving a bridge-tied load(e.g. a loudspeaker) that can be coupled between respective output nodes,of the first and second half-bridges,.

110 114 116 142 144 100 114 116 The first half-bridgecomprises a high-side switchcoupled in series with a complementary low-side switchbetween a first supply voltage (VDD) railand a reference voltage (e.g. ground) railof the output stage. The high-side switchand the low-side switchmay be, for example, complementary MOSFET devices.

120 124 126 142 144 100 124 126 Similarly, the second half-bridgecomprises a high-side switchcoupled in series with a complementary low-side switchbetween the first supply voltage (VDD) railand the reference voltage (e.g. ground) railof the output stage. Again, the high-side switchand the low-side switchmay be, for example, complementary MOSFET devices.

100 112 110 130 122 130 1 FIG. It will be appreciated by those skilled in the art that a practical implementation the switching driver circuitrymay include first output low-pass filter circuitry between the output nodeof the first half-bridgeand the loadand second output low-pass filter circuitry between the output nodeof the second half-bridge and the load. The first and second output low-pass filter circuitry are typically LC filters (i.e. comprise an inductor and a capacitor). Such filter circuitry is not shown infor the sake of clarity.

100 114 116 110 124 126 120 114 116 110 112 114 116 120 122 124 126 130 144 In use of the output stage, control signals such as pulse width modulated (PWM) signals are supplied to control terminals (e.g. gate terminals) of the high-side switchand low-side switchof the first half-bridge, and to control terminals (e.g. gate terminals) of the high-side switchand the low-side switchof the second half-bridge. The control signals are arranged such that when the high-side switchis switched on in response to a control signal at its control terminal, the low-side switchis switched off, and vice versa. Thus, in operation of the first half-bridge, the output nodewill be at either the first supply voltage (VDD) or the reference voltage (e.g. ground), depending upon whether the high-side switchor the low-side switchis switched on. Similarly, in operation of the second half-bridge, the output nodewill be at either the first supply voltage (VDD) or the reference voltage (e.g. ground), depending upon whether the high-side switchor the low-side switchis switched on. The output voltage VOut across the loadcan thus take any of three levels: +VDD, −VDD or 0V (assuming that the reference voltage railis coupled to ground).

100 114 116 124 126 114 116 124 126 100 In some low-power applications the output stagemay be implemented in integrated circuitry (e.g. in a single integrated circuit) comprising the switches,,,. In some examples, such integrated circuitry may also comprise modulator circuitry for supplying the control signals to the switches,,,of the output stage.

2 FIG. In higher power applications (e.g. automotive audio applications) it may be beneficial to use a single-ended output stage of the kind shown schematically in.

2 FIG. 200 210 212 214 222 224 200 212 214 As shown in, the single-ended output stagein this example comprises a half-bridgehaving a high-side switchcoupled in series with a complementary low-side switchbetween a first, positive (+VDD) supply voltage railand a second, negative (−VDD) supply voltage railof the single-ended output stage. The high-side switchand the low-side switchmay be, for example, complementary MOSFET devices.

200 230 216 210 226 200 240 242 244 216 230 210 212 214 2 FIG. In use of the single-ended output stage, a loadsuch as a loudspeaker is coupled between an output nodeof the half-bridgeand a reference voltage (e.g. ground) railof the single-ended output stage. In the example shown inlow-pass filter circuitrycomprising an inductorand a capacitoris coupled between the output nodeand the load, to attenuate high frequency components that may be present in an output signal of the half-bridgedue to the switching frequency of the switches,.

100 200 224 200 100 200 100 224 1 FIG. 2 FIG. 1 FIG. 2 FIG. Unlike the full bridge output stageof, the single-ended output stageofrequires a negative (−VDD) supply voltage rail. As will be appreciated by those skilled in the art, this may increase the complexity of the single-ended output stage, as compared to the full bridge output stageof. However, the single-ended output stagemay be more cost effective than the full bridge output stage. In particular, where multiple channels are required (e.g. in an application such as a multi-channel audio system where multiple different loads such as loudspeakers are to be driven) it may be more cost effective to use one single-ended output stage of the kind shown inper channel, with the negative (−VDD) supply voltage railbeing shared between all the channels, than to provide multiple full bridge output stages.

200 112 114 210 212 214 210 216 212 214 230 In operation of the single-ended output stage, control signals (e.g. PWM signals) are supplied to control terminals (e.g. gate terminals) of the high-side switchand low-side switchof the half-bridge. The control signals are arranged such that when the high-side switchis switched on in response to a control signal at its control terminal, the low-side switchis switched off, and vice versa. Thus, in operation of the half-bridge, the output nodewill be at either the first supply voltage (+VDD) or the second supply voltage (−VDD), depending upon whether the high-side switchor the low-side switchis switched on. The output voltage VOut across the loadcan thus take one of two levels: +VDD or −VDD.

200 212 214 212 214 240 242 244 240 200 In some examples the single-ended output stagemay be implemented in integrated circuitry (e.g. as a single integrated circuit incorporating the high-side switchand the low-side switch, and perhaps also modulator circuitry for generating the control signals that are supplied to the switches,), but the low-pass filter circuitryis typically implemented using discrete components that are not implemented in integrated circuitry—i.e. the inductorand capacitorof the low-pass filter circuitryare typically off-chip devices. However, in other examples the single-ended output stagemay be implemented entirely using off-chip devices, particularly in high-power applications where the cost of on-chip switches may be greater than that of off-chip switches.

3 FIG. 3 FIG. 300 310 312 314 322 324 316 310 340 342 344 330 326 is a schematic representation of switching driver circuitry capable of generating a three-level output voltage. In the example shown generally atin, the switching driver circuitry implements Class D amplifier circuitry, and includes a half-bridgecomprising a high-side switchand a low-side switchcoupled in series between a first, positive (+VDD) power supply railand a second, negative (−VDD) power supply rail, with an output nodeof the half-bridgebeing coupled, via low-pass filter circuitry(which comprises an inductorand a capacitor) to a first terminal of a load, the load having a second terminal coupled to a reference voltage (e.g. ground) rail.

300 350 326 316 310 3 FIG. The Class D amplifier circuitryoffurther comprises a third switch, having an input terminal coupled to the reference voltage (e.g. ground) railand an output terminal coupled to the output nodeof the half-bridge.

300 360 300 The Class D amplifier circuitryfurther comprises control circuitryconfigured to control a mode of operation of the Class D amplifier circuitry.

300 1 2 3 360 312 314 350 1 2 3 312 314 350 330 312 314 350 314 312 350 312 314 350 300 350 300 In use of the Class D amplifier circuitry, control signals C, C, Care supplied by the control circuitryto control terminals of the high-side switch, the low-side switchand the third switchrespectively. The control signals C, C, Care arranged such that only one of the high-side switch, the low-side switchand the third switchcan be switched on at once, so the output voltage VOut across the loadmay take one of three values: +VDD (when the high-side switchis switched on and the low-side switchand the third switchare both switched off), −VDD (when the low-side switchis switched on and the high-side switchand the third switchare both switched off), or 0V (when the high-side switchand the low-side switchare both switched off and the third switchis switched on). These three output voltage values may be used to encode three different values. For example, an output voltage of +VDD may represent a value of +1, an output voltage of −VDD may represent a value of −1 and an output voltage of 0 may represent a value of 0. The Class D amplifier circuitryis thus capable of operating in a first mode with two output voltage levels, if the third switchis held open (i.e. switched off). The Class D amplifier circuitrycan also operate in a second mode with three output voltage levels.

According to a first aspect, the invention provides switching driver circuitry comprising: a first half-bridge configured to switch a first supply voltage having a first magnitude; a second half-bridge configured to switch a second supply voltage having a second magnitude, wherein the first magnitude is greater than the second magnitude; and an isolation switch coupled to the first and second half-bridges and operable to isolate the second half-bridge from the first half-bridge.

The switching driver circuitry may further comprise control circuitry configured to control operation of the first and second half-bridges and the isolation switch in response to an input signal received by the control circuitry.

The switching driver circuitry may be operable in: a first mode in which the first half-bridge is operable to switch the first supply voltage; and a second mode in which the second half-bridge is operable to switch the second supply voltage, wherein the control circuitry is configured to control the mode of operation of the switching driver circuitry based on a level of the input signal.

The control circuitry may be configured to cause the switching driver circuitry to operate in the first mode if the level of the input signal is equal to or greater than a first threshold, and to cause the switching driver circuitry to operate in the second mode if the level of the input signal is less than the first threshold.

The switching driver circuitry may further comprise a ground switch coupled to an output node of the first half-bridge and operative to selectively couple the output node to ground.

The switching driver circuitry may further comprising a ground switch coupled to an output node of the first half-bridge and operative to selectively couple the output node to ground. The switching driver circuitry may be further operable in a quiescent mode in which the ground switch is actuated to couple the output node of the first half-bridge to ground. The control circuitry may be operative to select the quiescent mode if the level of the input signal is below a second threshold.

The first half-bridge may comprise a first high-side switch and a first low-side switch. The first high-side switch and the first low-side switch may comprise bandgap devices or high electron mobility transistor (HEMT) devices.

The first high-side switch and the first low-side switch may be Gallium Nitride (GaN) switches.

The second half-bridge may comprise a second high-side switch and a second low-side switch. The second high-side switch and the second low-side switch may comprise CMOS switches.

The isolation switch may comprise a bandgap device or a high electron mobility transistor (HEMT) device such as a GaN switch.

The switching driver circuitry may further comprise circuitry for deriving the second supply voltage from the first supply voltage.

The circuitry for deriving the second supply voltage from the first supply voltage may comprise low-dropout regulator (LDO) circuitry and/or charge pump circuitry.

The circuitry for deriving the second supply voltage from the first supply voltage may comprise: a reservoir capacitor coupled to the second half-bridge; and control circuitry operative to control the first and second half-bridges and the isolation switch to transfer charge to the reservoir capacitor from an external energy storage element.

The switching driver circuitry may further comprise a third half-bridge configured to switch a third supply voltage having a third magnitude, wherein the second magnitude is greater than the third magnitude.

According to a second aspect, the invention provides switching driver circuitry comprising: a first half-bridge configured to switch a first supply voltage having a first magnitude; a second half-bridge configured to switch the first supply voltage; a third half-bridge configured to switch a second supply voltage having a second magnitude, wherein the first magnitude is greater than the second magnitude; a fourth half-bridge configured to switch the second supply voltage, a first isolation switch coupled to the first and third half-bridges and operable to isolate the third half-bridge from the first half-bridge; and a second isolation switch coupled to the second and fourth half-bridges and operable to isolate the fourth half-bridge from the second half-bridge.

The switching driver circuitry may further comprise: first comparator circuitry configured to compare a first voltage at an output node of the first half-bridge to a first threshold and to prevent the first isolation switch from being switched on unless the voltage at the output node of the first half-bridge is below the first threshold; and second comparator circuitry configured to compare a second voltage at an output node of the second half-bridge to a second threshold and to prevent the second isolation switch from being switched on unless the second voltage at the output node of the second half-bridge is below the second threshold.

According to a third aspect, the invention provides an integrated circuit comprising: a low-power half-bridge comprising a high-side switch and a low-side switch coupled in series; and a half-bridge output terminal for coupling an output node of the low-power half-bridge to external high-power bridge circuitry, wherein the low-power half-bridge is configured to switch a low-power supply voltage having a first magnitude.

The integrated circuit may further comprise: control circuitry configured to control the high-side switch and the low-side switch of the low-power half-bridge and switches of the external high-power bridge circuitry; and control output terminals for coupling the control circuitry to control terminals of the external high-power bridge circuitry to permit operation of the high-power external bridge circuitry to be controlled by the control circuitry.

The high-side switch and the low-side switch may comprise CMOS switches.

The external high-power bridge circuitry may comprise a high-power half-bridge comprising a high-side switch and a low-side switch coupled in series. The high-power half-bridge may be configured to switch a high-power supply voltage having a second magnitude that is greater than the first magnitude. The external high-power bridge circuitry may further comprise an isolation switch configured to be coupled to the half-bridge output terminal and to selectively isolate the low-power half-bridge from the high-power half-bridge.

The high-side switch and the low-side switch of the external high-power bridge circuitry may comprise bandgap devices or high electron mobility transistor (HEMT) devices.

The high-side switch and the low-side switch of the external high-power bridge circuitry may be Gallium Nitride (GaN) switches.

The integrated circuit may further comprise a ground switch configured to selectively couple the output node of the low-power half-bridge to ground.

The low-power half-bridge may be operable to switch the low-power supply voltage in response to control signals received from control circuitry when a level of an input signal received by the control circuitry is below a first threshold.

The integrated circuit may further comprise circuitry for deriving the low-power supply voltage from the high-power supply voltage.

The circuitry for deriving the low-power supply voltage from the high-power supply voltage may comprise low-dropout regulator (LDO) circuitry and/or charge pump circuitry.

The circuitry for deriving the low-power supply voltage from the high-power supply voltage may comprise: a reservoir capacitor coupled to the second half-bridge; and control circuitry operative to control the first and second half-bridges and the isolation switch to transfer charge to the reservoir capacitor from an external energy storage element.

The integrated circuit may further comprise a further half-bridge comprising a high-side switch and a low-side switch coupled in series and configured to switch a third supply voltage having a third magnitude.

According to a fourth aspect, the invention provides driver integrated circuit comprising: an internal half-bridge capable of switching a first voltage; a ground switch; and control circuitry, wherein the control circuitry is configured to control operation of the internal half-bridge, the ground switch and an external half-bridge that is capable of switching a second voltage of higher magnitude than the first voltage.

According to a fifth aspect, the invention provides driver integrated circuit comprising: a first internal half-bridge capable of switching a first voltage; a second internal half-bridge capable of switching a first voltage; and control circuitry, wherein the control circuitry is configured to control operation of the first and second internal half-bridges, and first and second external half-bridges that are capable of switching a second voltage of higher magnitude than the first voltage.

According to a sixth aspect, the invention provides a host device comprising the driver integrated circuit of the fourth or fifth aspect.

The host device may comprise a laptop, notebook, netbook or tablet computer, a gaming device, a games console, a controller for a games console, a virtual reality (VR) or augmented reality (AR) device, a mobile telephone, a portable audio player, a portable device, an accessory device for use with a laptop, notebook, netbook or tablet computer, a gaming device, a games console a VR or AR device, a mobile telephone, a portable audio player or other portable device.

Throughout this specification the word “comprise”, or variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.

312 314 310 350 300 312 314 312 314 3 FIG. In low-power applications such as portable audio devices, the switches,of the half-bridgeand the third switchof the Class D amplifier circuitryofmay be implemented by CMOS devices such as MOSFETs. For higher power applications such as automotive audio applications, where the switches,may be required to switch relatively high voltages (e.g. greater than 60 volts DC), it may not be feasible to implement the switches,of the half-bridge with CMOS devices, due to limitations in the maximum drain to source voltage (Vds) that can be supported by such devices and the high complexity of analog design for CMOS processes operating at such voltages.

312 314 310 2 3 Thus, in such higher power applications the switches,of the half-bridgemay be implemented using devices that are capable of supporting higher voltages, such as wide bandgap devices or high electron mobility transistor (HEMT) devices based on, for example, Gallium Nitride (GaN), Silicon Carbide (SiC), Gallium Oxide (Ga0) or other semiconductor materials. Such devices are typically capable of operation at higher voltages, higher temperatures and higher frequencies than silicon-based switches such as MOSFETs.

300 1 2 312 314 310 300 3 FIG. However, the use of higher supply voltages can limit the dynamic range of the switching driver circuitry. In general, the output voltage VOut of three-level Class D amplifier circuitry of the kind shown generally atinis defined by the product of a duty cycle d of the control signals C, Capplied to the switches,of the half-bridgeand the supply voltage, i.e. VOut=d×VDD. It follows from this that accurate control of the output voltage VOut requires that the duty cycle d is variable between a very low value (i.e. theon-pulses of very short duration) and a much higher value (i.e. on-pulses of much longer duration). For example, if an output voltage VOut of 1 millivolt were required from the Class D amplifier circuitryand the supply voltage VDD were 100 volts, a duty cycle d of 0.00001 would be required, whereas an output voltage VOut of 50 volts would require a much lower duty cycle d of 0.5.

4 FIG. is a schematic representation of switching driver circuitry according to the present disclosure.

400 410 412 414 422 1 424 1 4 FIG. In the example shown generally atin, the switching driver circuitry implements Class D amplifier circuitry, and includes a first half-bridgecomprising a first high-side switchand a first low-side switchcoupled in series between a first positive power supply railthat receives a first positive power supply voltage +VSupfrom a power supply (not shown) and a first negative power supply railthat receives a first negative power supply voltage −VSupfrom the power supply.

410 1 1 412 414 412 414 412 414 2 3 The first half-bridgeis configured to switch relatively high voltages, and may thus be termed a “high-power half-bridge”. For example, the magnitude of the first positive power supply voltage +VSupand the first negative power supply voltage −VSupmay be of the order of 60 volts or more. The first high-side switchand the first low-side switchare capable of supporting such relatively high voltages. The first high-side switchand the first low-side switchmay be, for example, wide bandgap devices or high electron mobility transistor (HEMT) devices based on, for example, Gallium Nitride (GaN), Silicon Carbide (SIC), Gallium Oxide (Ga0) or other semiconductor materials. In a particular example, the high-side switchand the low-side switchare GaN switches.

400 430 432 434 442 2 444 2 2 1 The switching driver circuitryfurther includes a second half-bridgecomprising a second high-side switchand a second low-side switchcoupled in series between a second positive power supply railthat receives a second positive power supply voltage +VSupand a second negative power supply railthat receives a second negative power supply voltage −VSup. The second power supply voltages +/−VSupmay be derived from the first power supply voltages +/−VSupas will be explained below.

420 410 2 2 432 434 The second half-bridgeis configured to switch lower voltages than the first half-bridge, and may thus be termed a “low-power half-bridge”. For example, the magnitude of the second positive power supply voltage +VSupand the second negative power supply voltage −VSupmay be of the order of 12 volts or less. The second high-side switchand the second low-side switchare capable of supporting such voltages and may be implemented, for example, using silicon-based MOSFETS.

400 450 452 436 430 432 434 450 The switching driver circuitryfurther comprises a ground switch, having an input terminal coupled to a ground railthat receives a ground reference voltage (i.e. 0 volts) and an output terminal coupled to an output nodeof the second half-bridge, between the second high-side switchand the second low-side switch. The ground switchmay be implemented, for example, using a CMOS device such as a silicon-based MOSFET.

400 460 436 430 416 410 412 424 460 430 410 1 1 432 434 430 430 460 422 424 460 410 430 460 460 412 424 410 412 424 410 460 2 3 The switching driver circuitryfurther comprises an isolation switch, having an input terminal coupled to the output nodeof the second half-bridgeand an output terminal coupled to an output nodeof the first half-bridge, between the first high-side switchand the second high-side switch. The isolation switchis operable to isolate the second half-bridgefrom the first half-bridge, such that the first positive and negative supply voltages +VSup, −VSup(which could damage the switches,of the second half-bridge) are not transmitted to the second half-bridge. The isolation switchis capable of supporting relatively high voltages of the kind supplied by the first positive and negative supply rails,. In particular, the isolation switchis configured such that, when switched off, such relatively high voltages cannot pass from the first half-bridgeto the second half-bridge. The isolation switchmay be, for example, a wide bandgap device or a high electron mobility transistor (HEMT) device based on, for example, Gallium Nitride (GaN), Silicon Carbide (SiC), Gallium Oxide (Ga0) or other semiconductor materials. The isolation switchneed not be of the same type as the switches,of the first half-bridge. For example, the switches,of the first half-bridgemay be GaN switches, and the isolation switchmay be a SiC switch.

400 416 410 470 472 474 476 476 478 In use of the switching driver circuitry, the output nodeof the first half-bridgeis coupled, via low-pass filter circuitry(which comprises an inductorand a capacitor) to a first terminal of a load, the loadhaving a second terminal coupled to a reference voltage (e.g. ground) rail.

400 480 400 480 400 The switching driver circuitryfurther comprises control circuitry(which may also be referred to as modulator circuitry) configured to control the operation of the switching driver circuitrybased on an input signal SIn, received by the control circuitry, that represents a signal to be amplified by the switching driver circuitry.

400 1 2 480 412 414 412 414 3 4 5 480 432 434 450 432 434 450 6 480 460 460 In use of the switching driver circuitry, control signals C, Care supplied by the control circuitryto control terminals of the first high-side switchand the first low-side switch, respectively, to control operation of the first and second high-side switches,. Similarly, control signals C, C, Care supplied by the control circuitryto control terminals of the second high-side switch, the second low-side switchand the ground switch, respectively, to control operation of the second high-side switch, the second low-side switchand the ground switch. A further control signal Cis supplied by the control circuitryto the isolation switch, to control operation of the isolation switch.

400 460 410 1 1 476 6 460 460 430 410 1 2 480 412 414 476 410 1 412 414 1 414 412 3 4 432 434 432 434 5 450 450 The switching driver circuitryis operable in a first mode (which may be referred to as a high-power output mode) in which the isolation switchis open (switched off) and the first half-bridgesupplies either the first positive supply voltage +VSupor the first negative supply voltage −VSupto the load. In the first mode, the control signal Cis supplied to the isolation switchto turn the isolation switchoff, thus decoupling and isolating the second half-bridgefrom the first half-bridge. The control signals C, Coutput by the control circuitryin the first mode are arranged such that only one of the first high-side switchand the first low-side switchcan be switched on at once. Thus, in the first mode, the output voltage VOut supplied across the loadby the first half-bridgemay take one of two values: +VSup(when the first high-side switchis switched on and the first low-side switchis switched off), and −VSup(when the first low-side switchis switched on and the first high-side switchis switched off). In the first mode, the control signals C, Csupplied to the second high-side switchand the second low-side switch, respectively, may cause the second high-side switchand the second low-side switchto be held open (i.e. switched off), and the control signal Csupplied to the ground switchmay cause the ground switchto be closed (i.e. switched on).

400 460 6 430 450 2 2 476 6 460 460 436 430 476 470 3 4 5 480 432 434 450 486 430 450 2 432 434 450 2 434 432 450 432 434 450 1 2 412 414 412 414 The switching driver circuitryis also operable in a second mode (which may be referred to as a low-power output mode), in which the isolation switchis closed (i.e. switched on) in response to a suitable control signal C, and the combination of the second half-bridgeand the ground switchsupplies either the second positive supply voltage +VSup, 0V, or the second negative supply voltage −VSupto the load. In the second mode, the control signal Cis supplied to the isolation switchto turn the isolation switchon, thus coupling the output nodeof the second half-bridgeto the load(via the low-pass filter). The control signals C, C, Coutput by the control circuitryin the second, low-power output mode are arranged such that only one of the second high-side switch, the second low-side switchand the ground switchcan be switched on at once. Thus, in the second mode, the output voltage VOut supplied across the loadby the combination of the second half-bridgeand the ground switchmay take one of three values: +VSup(when the second high-side switchis switched on and the second low-side switchand the ground switchare both switched off), −VSup(when the second low-side switchis switched on and the second high-side switchand the ground switchare both switched off), and 0V (when the second high-side switchand the second low-side switchare switched off and the ground switchis switched on). In the second mode, the control signals C, Csupplied to the first high-side switchand the first low-side switch, respectively, may cause the first high-side switchand the first low-side switchto be held open (i.e. switched off).

480 400 480 480 400 The control circuitryis configured to control the mode of operation of the switching driver circuitrybased on a level (e.g. a magnitude, envelope or volume) of the input signal SIn received by the control circuitry. The control circuitrymay be configured to compare the level if the input signal SIn to a first threshold and, based on the result of this comparison, cause the switching driver circuitryto operate in either its first (high-power output) mode or its second (low-power output) mode.

476 2 476 430 For example, if the level of the input signal SIn is equal to or greater than the first threshold, this may be indicative that an output voltage VOut across the loadof a magnitude greater than that of the second supply voltage VSupis required for the loadto generate an output signal of a desired magnitude (e.g. an audio output of a desired volume) and thus cannot be supplied by the second half-bridge.

480 400 6 460 1 2 412 414 476 Thus, if the level of the input signal Sin is equal to or greater than the first threshold, the control circuitrymay cause the switching driver circuitryto operate in its first (high-power output) mode, by outputting a suitable control signal Cto switch off the isolation switchand outputting suitable control signals C, Cto control the first high-side switchand the first low-side switchto generate the required output voltage VOut across the load.

476 476 2 430 In contrast, if the level of the input signal SIn is lower than the first threshold, this may be indicative that the magnitude of the output voltage VOut across the loadrequired for the loadto generate an output signal of a desired magnitude (e.g. an audio output of a desired volume) is less than (or equal to) that of the second supply voltage VSupand can thus be supplied by the second half-bridge.

480 400 6 460 3 4 5 432 434 450 476 Thus, if the level of the input signal is less than the first threshold, the control circuitrymay cause the switching driver circuitryto operate in its second (low-power output) mode, by outputting a suitable control signal Cto switch on the isolation switch, and outputting suitable control signals C, C, Cto control the second high-side switch, the second low-side switchand the ground switchto generate the required output voltage VOut across the load.

400 476 If the level of the input signal is zero (or less than a second threshold that is lower than the first threshold), this may be indicative that no output signal is required, such that the switching driver circuitrycan operate in a quiescent mode in which no output voltage VOut is supplied to the load.

480 6 460 5 450 1 2 3 4 412 414 432 434 412 414 432 434 450 460 416 410 476 Thus, if the level of the input signal is zero (or less than the second threshold), the control circuitrymay output a suitable control signal Cto switch on the isolation switch, and output a suitable control signal Cto switch on the ground switch, and output suitable control signals C, C, C, Cto switch off the first high-side switch, the first low-side switch, the second high-side switchand the second low-side switch. With the switches,,,,,in this configuration, the output nodeof the first half-bridgeis coupled to ground, such that no output voltage VOut develops across the load. This effectively implements a mute mode for extremely small input signals.

400 400 476 1 4 412 414 432 434 410 430 4 FIG. By selecting between the first (high-power output) mode and the second (low-power output) mode based on the level of the input signal SIn, the switching driver circuitryofis capable of efficiently supplying a highly accurate output voltage over a wide range. In particular, operating the Class D amplifier circuitryin its second mode when the level of the input signal SIn is less than the first threshold (and in the quiescent mode when the input signal level is zero or less than the second threshold) and in its first mode when the level of the input signal SIn is equal to or greater than the first threshold ensures that there is minimal unnecessary headroom in the supply voltage that is switched to provide the output voltage VOut to the load, while also enabling highly accurate control of the magnitude of the output voltage without requiring excessively low duty cycles for the control signals C-Cthat control the switches,,,of the first and second half-bridges,.

400 430 2 2 432 434 400 410 1 1 432 434 For example, if an output voltage VOut of 1 millivolt were required, the switching driver circuitrywould operate in its second mode using the second half-bridgeto switch the second supply voltage +/−VSup. If the magnitude of VSupwere 10 volts, a duty cycle d of 0.0001 would be required for switching the switches,. In contrast, if an output voltage VOut of 50 volts were required, the switching driver circuitrywould operate in its first mode using the first half-bridgeto switch the first supply voltage +/−VSup. If the magnitude of VSupwere 100 volts, a duty cycle d of 0.5 would be required for switching the switches,.

430 450 480 490 410 460 490 432 434 450 490 480 490 492 436 460 494 494 480 412 414 410 a c In some examples, the second half-bridge, the ground switchand the control circuitrymay be provided on a single IC, while the first half-bridgeand the isolation switchare external to the IC. In such examples, the control terminals of the second high-side switch, second low-side switchand ground switchmay be coupled, internally of the IC, to appropriate outputs of the control circuitry, and the ICmay be provided with a half-bridge output terminalfor coupling the output nodeto the input terminal of the external isolation switch, and with control output terminals-for coupling outputs of the control circuitryto control terminals of the first high-side switchand the first low-side switchof the external first half-bridge.

430 2 450 480 480 430 450 410 1 Thus, such an IC includes an internal half-bridge (the second half-bridge) capable of switching a first voltage (the second supply voltage VSup), the ground switch, and the control circuitry. The control circuitryis configured to control operation of the internal half-bridge, the ground switchand an external half-bridge (the first half-bridge) that is capable of switching a second voltage (the first supply voltage VSup) of higher magnitude than the first voltage.

480 410 4 FIG. Such an IC (which may be referred to as a “bridge driver IC” or simply a “driver IC” or an “amplifier IC”) is thus capable of operation, in relatively low-power applications, as a standalone driver for driving a load such as an audio output transducer (e.g. a speaker), a haptic output transducer (e.g. a resonant actuator) or the like with a two- or three-level signal, or in combination with another such IC in a bridge-tied load configuration for driving such a load. Additionally, because such an IC includes the control circuitry, it is also capable of operation, in higher-power applications, for controlling an external high-power output stage such as the first half-bridgedescribed above with reference to.

430 450 490 480 490 410 460 490 3 4 5 432 434 450 480 492 436 460 In other examples, the second half-bridgeand the ground switchmay be provided on a single integrated circuit (IC), but the control circuitrymay be external to the IC, as well as the first half-bridgeand the isolation switch. In such examples, the ICis provided with input terminals for receiving the control signals C, Cand Cfor the second high-side switch, the second low-side switchand the ground switchfrom the external control circuitry, and with a half-bridge output terminalfor coupling the output nodeto the input terminal of the external isolation switch.

5 FIG. is a schematic representation of alternative switching driver circuitry according to the present disclosure.

500 400 5 FIG. 4 FIG. 4 5 FIGS.and The alternative switching driver circuitry shown generally atinis similar to, and has a number of elements in common with the switching driver circuitryof. Such common elements are denoted by common reference numerals inand will not be described in detail here, for the sake of clarity and brevity.

500 400 450 500 476 436 430 2 2 432 434 5 FIG. 4 FIG. The alternative switching driver circuitryofdiffers from the switching driver circuitryofin that it does not include the ground switch. Thus, when operating in the second (low-power output) mode of operation, the alternative switching driver circuitrycan supply only a two-level output voltage VOut to the load, by switching the output nodeof the second half-bridgebetween the second positive supply voltage +VSupand the second to negative supply voltage −VSupby appropriate control of the second high-side switchand the second low-side switch.

500 500 400 4 FIG. Thus the alternative switching driver circuitryis not able to operate in the quiescent mode described above with reference towhen the level of the input signal Sin is zero or less than a second threshold, and thus the quiescent power consumption of the alternative switching driver circuitrymay be greater than that of the switching driver circuitry.

500 400 476 430 450 400 430 476 500 4 FIG. 5 FIG. However, the alternative switching driver circuitryis simpler than the switching driver circuitry, as a feedback loop may be required in order to avoid or suppress distortion in the output generated by the loadin the three-level arrangement provided by the combination of the second half-bridgeand the ground switchof the switching driver circuitryof. In contrast, the two-level arrangement provided by the second half-bridgeof(without a ground switch) is capable of open-loop operation without introducing distortion in the output generated by the load. Thus, the alternative switching driver circuitryrepresents a compromise between reduced design complexity and increased quiescent power consumption.

2 2 As will be appreciated by those of ordinary skill in the art, the second positive and negative supply voltages +VSup, −VSupcan be generated in a variety of different ways.

6 FIG. 6 FIG. 2 2 1 1 600 610 1 1 2 620 442 620 2 444 is a schematic representation of an arrangement for generating the second positive and negative supply voltages +VSup, −VSupfrom the first positive and negative supply voltages +VSup, −VSup. In the arrangement shown generally atin, low drop-out regulator (LDO) circuitryreceives the first positive and negative supply voltages +VSup, −VSupand generates the second positive supply voltage +VSup, which is supplied to charge pump circuitryand to the second positive power supply rail. The charge pump circuitrygenerates the second negative supply voltage −VSup, and outputs it to the second negative power supply rail.

2 2 1 1 1 2 2 2 1 1 1 2 2 2 1 1 1 2 The second positive and negative supply voltages +VSup, −VSupmay be between 0.1× and 0.3× the first positive and negative supply voltages +VSup, −VSup(i.e. if +/−VSupis 100 volts, +/−VSupis between 10 volts and 30 volts). In some examples, the second positive and negative supply voltages +VSup, −VSupare of the order of 0.2× the first positive and negative supply voltages +VSup, −VSup(i.e. if +/−VSupis 100 volts, +/−VSupis of the order of 20 volts). In other examples, the second positive and negative supply voltages +VSup, −VSupare of the order of one-sixth of the first positive and negative supply voltages +VSup, −VSup(i.e. if +/−VSupis 100 volts, +/−VSupis of the order of 16.67 volts).

610 490 430 490 6 FIG. The LDO circuitrymay be implemented as part of an ICthat also implements the second half-bridge, as shown in, or alternatively may be external to the IC.

7 FIG. 7 FIG. 2 2 1 1 700 710 1 1 2 2 442 444 is a schematic representation of an alternative arrangement for generating the second positive and negative supply voltages +VSup, −VSupfrom the first positive and negative supply voltages +VSup, −VSup. In the arrangement shown generally atin, charge pump circuitryreceives the first positive and negative supply voltages +VSup, −VSupand outputs the second positive and negative supply voltages +VSup, −VSupto the second positive power supply railand the second negative power supply rail, respectively.

2 2 1 1 1 2 2 2 1 1 1 2 2 2 1 1 1 2 Again, the second positive and negative supply voltages +VSup, −VSupmay be between 0.1× and 0.3× the first positive and negative supply voltages +VSup, −VSup(i.e. if +/−VSupis 100 volts, +/−VSupis between 10 volts and 30 volts). In some examples, the second positive and negative supply voltages +VSup, −VSupare of the order of 0.2× the first positive and negative supply voltages +VSup, −VSup(i.e. if +/−VSupis 100 volts, +/−VSupis of the order of 20 volts). In other examples, the second positive and negative supply voltages +VSup, −VSupare of the order of one-sixth of the first positive and negative supply voltages +VSup, −VSup(i.e. if +/−VSupis 100 volts, +/−VSupis of the order of 16.67 volts). Those skilled in the art will be familiar with charge pump topologies that can generate an output voltage that is between 0.1× and 0.3× its input voltage, an output voltage that is of the order of 0.2× its input voltage, and an output voltage that is of the order of one-sixth of its input voltage.

710 490 430 490 7 FIG. The charge pump circuitrymay be implemented as part of an ICthat also implements the second half-bridge, as shown in, or alternatively may be external to the IC.

In some applications it may be desirable to provide more than two half-bridges, with each half-bridge being configured to switch a supply voltage of a different magnitude.

8 FIG. 800 is a schematic representation of example switching driver circuitryincluding three half-bridges, but it will be appreciated that the principles described below are equally applicable to switching driver circuitry including four or more half-bridges.

800 410 1 410 430 460 8 FIG. 4 FIG. 4 FIG. 4 FIG. The switching driver circuitryofimplements Class D amplifier circuitry, and includes a first half-bridgeof the kind described above with reference to, configured to switch a relatively high supply voltage +/−VSup. The first half-bridgeis coupled to a second half-bridgeof the kind described above with reference to, by an isolation switchof the kind described above with reference to.

800 830 832 834 842 3 3 3 2 2 3 832 834 830 432 434 The switching driver circuitryfurther comprises a third half-bridge, comprising a third high-side switchand a third low-side switchcoupled in series between a third positive power supply railwhich receives a third positive power supply voltage +VSupand a third negative power supply rail which receives a third negative power supply voltage −VSup. The third positive and negative power supply voltages +/−VSupmay be of lower magnitude than the second positive and negative power supply voltages +/VSup. For example, if the magnitude of +/−VSupis 12 volts, the magnitude of +/−VSupmay be 5 volts. The switches,of the third half-bridgeare typically able to support lower maximum drain to source voltages (Vds) than the switches,of the second half-bridge.

436 430 836 832 834 830 840 836 830 852 852 840 850 436 430 852 The output nodeof the second half-bridgeis coupled to an output node(between the third high-side switchand the third low-side switch) of the third half-bridgeby coupling switch. The output nodeof the third half-bridgeis also coupled to a ground (i.e. 0V) supply railby a ground switch. Thus, when the coupling switchand the ground switchare both switched on, the output nodeof the second half-bridgeis coupled to the ground supply rail.

800 880 800 800 880 The switching driver circuitryfurther comprises control circuitry(which may also be referred to as modulator circuitry) configured to control the operation of the switching driver circuitry, based on an input signal SIn, representing a signal to be amplified by the switching driver circuitry, received by the control circuitry.

800 1 2 880 412 414 412 414 3 4 5 880 432 434 840 432 434 840 6 880 460 460 7 8 9 880 832 834 850 In use of the switching driver circuitry, control signals C, Care supplied by the control circuitryto control terminals of the first high-side switchand the first low-side switch, respectively, to control operation of the first and second high-side switches,. Similarly, control signals C, C, Care supplied by the control circuitryto control terminals of the second high-side switch, the second low-side switchand the coupling switch, respectively, to control operation of the second high-side switch, the second low-side switchand the coupling switch. A further control signal Cis supplied by the control circuitryto the isolation switchto control operation of the isolation switch, and further control signals C, C, Care supplied by the control circuitryto control terminals of the third high-side switch, the third low-side switchand the ground switchto control operation of those switches.

800 460 410 1 1 476 6 460 460 430 410 1 2 480 412 414 476 410 1 412 414 1 414 412 3 4 432 434 432 434 5 840 840 7 8 832 834 832 834 9 850 850 The switching driver circuitryis operable in a first (high-power output) mode in which the isolation switchis open (switched off) and the first half-bridgesupplies either the first positive supply voltage +VSupor the first negative supply voltage −VSupto the load. In the first mode, the control signal Cis supplied to the isolation switchto turn the isolation switchoff, thus decoupling and isolating the second half-bridgefrom the first half-bridge. The control signals C, Coutput by the control circuitryin the first mode are arranged such that only one of the first high-side switchand the first low-side switchcan be switched on at once. Thus, in the first mode, the output voltage VOut supplied across the loadby the first half-bridgemay take one of two values: +VSup(when the first high-side switchis switched on and the first low-side switchis switched off), or −VSup(when the first low-side switchis switched on and the first high-side switchis switched off). In the first mode, the control signals C, Csupplied to the second high-side switchand the second low-side switch, respectively, may cause the second high-side switchand the second low-side switchto be held open (i.e. switched off), and the control signal Csupplied to the coupling switchmay cause the coupling switchto be closed (i.e. switched on). Similarly, the control signals C, Csupplied to the third high-side switchand the third low-side switch, respectively, may cause the third high-side switchand the third low-side switchto be held open (i.e. switched off), and the control signal Csupplied to the second ground switchmay cause the second ground switchto be closed (i.e. switched on).

800 460 6 430 840 850 2 2 476 6 460 460 436 430 476 470 3 4 5 9 480 432 434 840 850 476 430 840 850 2 432 434 840 850 2 434 432 840 850 432 434 840 850 1 2 412 414 412 414 7 8 832 834 832 834 The switching driver circuitryis also operable in a second (lower-power output) mode, in which the isolation switchis closed (i.e. switched on) in response to a suitable control signal C, and the combination of the second half-bridgeand the coupling switchand the ground switchsupplies either the second positive supply voltage +VSup, 0V, or the second negative supply voltage −VSupto the load. In the second mode, the control signal Cis supplied to the isolation switchto turn the isolation switchon, thus coupling the output nodeof the second half-bridgeto the load(via the low-pass filter). The control signals C, C, C, Coutput by the control circuitryin the second mode are arranged such that only one of the second high-side switch, the second low-side switchand the combination of the coupling switchand the ground switchcan be switched on at once. Thus, in the second mode, the output voltage VOut supplied across the loadby the combination of the second half-bridgeand the coupling switchand the ground switchmay take one of three values: +VSup(when the second high-side switchis switched on and the second low-side switch, the coupling switchand the ground switchare all switched off), −VSup(when the second low-side switchis switched on and the second high-side switchand the coupling switchand the ground switchare all switched off), or 0V, when the second high-side switchand the second low-side switchare switched off and the coupling switchand the ground switchare switched on. In the second mode, the control signals C, Csupplied to the first high-side switchand the first low-side switch, respectively, may cause the first high-side switchand the first low-side switchto be held open (i.e. switched off). Similarly, the control signals C, Csupplied to the third high-side switchand the third low-side switchmay cause the third high-side switchand the third low-side switchto be held open (i.e. switched off).

800 460 6 830 850 3 3 476 6 460 460 5 840 840 836 830 476 470 7 8 9 880 832 834 850 476 830 850 3 832 834 850 3 834 832 850 832 834 850 1 2 412 414 412 414 3 4 432 434 432 434 The switching driver circuitryis also operable in a third (lowest-power output) mode, in which the isolation switchis closed (i.e. switched on) in response to a suitable control signal C, and the combination of the third half-bridgeand the ground switchsupplies either the third positive supply voltage +VSup, 0V, or the third negative supply voltage −VSupto the load. In the third mode, the control signal Cis supplied to the isolation switchto turn the isolation switchon, and the control signal Cis supplied to the coupling switchto turn the coupling switchon, thus coupling the output nodeof the third half-bridgeto the load(via the low-pass filter). The control signals C, C, Coutput by the control circuitryin the third mode are arranged such that only one of the third high-side switch, the third low-side switchand the ground switchcan be switched on at once. Thus, in the third mode, the output voltage VOut supplied across the loadby the combination of the third half-bridgeand the ground switchmay take one of three values: +VSup(when the third high-side switchis switched on and the third low-side switchand the ground switchare both switched off), −VSupl(when the third low-side switchis switched on and the third high-side switchand the ground switchare both switched off), and 0V (when the third high-side switchand the third low-side switchare switched off and the ground switchis switched on). In the third mode, the control signals C, Csupplied to the first high-side switchand the first low-side switch, respectively, may cause the first high-side switchand the first low-side switchto be held open (i.e. switched off). Similarly, the control signals C, Csupplied to the second high-side switchand the second low-side switchmay cause the second high-side switchand the second low-side switchto be held open (i.e. switched off).

832 834 830 410 430 410 430 800 416 832 834 800 416 3 3 3 As the switches,of the third half-bridgeare “weaker” than those of the first and second half-bridges,, in that they are only capable of supporting drain to source voltages (Vds) that are lower than those that can be supported by the first and second half-bridges,, it is important, when operating the switching driver circuitryin the third (lowest-power output) mode that the voltage at the output nodeis small enough that it will not cause damage to the switches,. Thus, in operation of the switching driver circuitry, the voltage at the output nodeshould remain within the limits of the third power supply voltage VSup(i.e. between −VSupand +VSup).

800 1 2 412 414 412 414 3 4 432 434 432 434 416 3 To this end, in operation of the switching driver circuitry, In the second mode, the control signals C, Csupplied to the first high-side switchand the first low-side switch, respectively, may cause the first high-side switchand the first low-side switchto be held open (i.e. switched off). Similarly, the control signals C, Csupplied to the second high-side switchand the second low-side switchmay cause the second high-side switchand the second low-side switchto be held open (i.e. switched off), such that the voltage at the output nodenever exceeds +/−VSup.

880 880 880 800 The control circuitryis configured to control the mode of operation of the switching driver circuitry based on a level (e.g. a magnitude or envelope) of the input signal SIn received by the control circuitry. The control circuitrymay be configured to compare the level of the input signal SIn to first and second thresholds (where the second threshold is lower than the first threshold), and based on the results of these comparisons, cause the switching driver circuitryto operate in either its first (high-power output) mode, its second (lower-power output) mode, or its third (lowest-power output) mode.

476 2 476 430 For example, if the level of the input signal Sin is equal to or greater than the first threshold, this may be indicative that an output voltage VOut across the loadof a magnitude greater than that of the second supply voltage VSupis required for the loadto generate an output signal of a desired magnitude (e.g. an audio output of a desired volume) and thus cannot be supplied by the second half-bridge.

880 800 6 460 1 2 412 414 476 Thus, if the level of the input signal Sin is equal to or greater than the first threshold, the control circuitrymay cause the switching driver circuitryto operate in its first (high-power output) mode by outputting a suitable control signal Cto switch off the isolation switchand outputting suitable control signals C, Cto control the first high-side switchand the first low-side switchto generate the required output voltage VOut across the load.

476 476 2 3 430 If the level of the input signal Sin is lower than the first threshold, but equal to or greater than the second threshold, this may be indicative that the magnitude of the output voltage VOut across the loadrequired for the loadto generate an output signal of a desired magnitude (e.g. an audio output of a desired volume) is less than (or equal to) that of the second supply voltage VSupbut greater than that of the third supply voltage VSup, and can thus be supplied by the second half-bridge.

880 800 6 460 3 4 5 9 432 434 840 850 476 Thus, if the level of the input signal is less than the first threshold but equal to or greater than the second threshold, the control circuitrymay may cause the switching driver circuitryto operate in its second (lower-power output) mode by outputting a suitable control signal Cto switch on the isolation switch, and outputting suitable control signals C, C, C, Cto control the second high-side switch, the second low-side switchand the coupling switchand the ground switchto generate the required output voltage VOut across the load.

476 476 3 830 If the level of the input signal Sin is lower than the second threshold, this may be indicative that the magnitude of the output voltage VOut across the loadrequired for the loadto generate an output signal of a desired magnitude (e.g. an audio output of a desired volume) is less than (or equal to) that of the third supply voltage VSup, and can thus be supplied by the third half-bridge.

880 800 6 460 7 8 9 832 834 850 476 Thus, if the level of the input signal is less than the second threshold, the control circuitrymay may cause the switching driver circuitryto operate in its third (lowest-power output) mode, by outputting a suitable control signal Cto switch on the isolation switch, and outputting suitable control signals C, C, Cto control the third high-side switch, the third low-side switchand the ground switchto generate the required output voltage VOut across the load.

800 476 880 6 460 5 9 840 850 1 2 3 4 7 8 412 414 432 434 832 834 412 414 432 434 840 460 832 834 850 416 410 476 If the level of the input signal is zero (or less than a third threshold that is lower than the second threshold), this may be indicative that no output signal is required, such that the switching amplifier circuitrycan operate in a quiescent mode in which no output voltage VOut is supplied to the load. Thus, if the level of the input signal is zero (or less than the third threshold), the control circuitrymay output a suitable control signal Cto switch on the isolation switch, and may output suitable control signals C, Cto switch on the coupling switchand the ground switch, and may output suitable control signals C, C, C, C, C, Cto switch off the first high-side switch, the first low-side switch, the second high-side switch, the second low-side switch, the third high-side switchand the third low-side switch. With the switches,,,,,,,,in this configuration, the output nodeof the first half-bridgeis coupled to ground, such that no output voltage VOut develops across the load.

8 FIG. 800 476 1 4 7 8 412 414 432 434 832 834 410 430 830 By selecting between the first (high-power output) mode, the second (lower-power output) mode and the third (lowest-power output) mode based on the level of the input signal SIn, the switching driver circuitry ofis capable of efficiently supplying a highly accurate output voltage over a wide range. In particular, operating the Class D amplifier circuitryin its second (lower-power output) mode when the level of the input signal SIn is less than the first threshold and in its third (lowest-power output) mode when the level of the input signal Sin is less than the second threshold (and in the quiescent mode when the input signal level is zero or less than the third threshold) and in its first (high-power output) mode when the level of the input signal Sin is equal to or greater than the first threshold ensures that there is minimal unnecessary headroom in the supply voltage that is switched to provide the output voltage VOut to the load, while also enabling highly accurate control of the magnitude of the output voltage without requiring excessively low duty cycles for the control signals C-C, C, Cthat control the switches,,,,,, of the first, second and third half-bridges,,.

430 830 840 850 880 890 410 460 890 432 434 832 834 840 850 890 480 890 492 436 460 494 494 880 412 414 410 a c In some examples, the second and third half-bridges,, the coupling switch, the ground switchand the control circuitrymay be provided on a single IC, while the first half-bridgeand the isolation switchare external to the IC. In such examples, the control terminals of the second high-side switch, second low-side switch, the third high-side switch, the third low-side switch, the coupling switchand the ground switchmay be coupled, internally of the IC, to appropriate outputs of the control circuitry, and the ICmay be provided with a half-bridge output terminalfor coupling the output nodeto the input terminal of the external isolation switch, and with control output terminals-for coupling outputs of the control circuitryto control terminals of the first high-side switchand the first low-side switchof the external first half-bridge.

430 830 840 850 890 880 890 410 460 890 3 4 7 8 5 9 432 434 832 834 840 850 880 492 436 460 In other examples, the second and third half-bridges,, the coupling switchand the ground switchmay be provided on a single integrated circuit (IC), but the control circuitrymay be external to the IC, as well as the first half-bridgeand the isolation switch. In such examples, the ICis provided with input terminals for receiving the control signals C, C, C, C, Cand Cfor the second high-side switch, the second low-side switch, the third high-side switch, the third low-side switch, the coupling switchand the ground switchfrom the external control circuitry, and with a half-bridge output terminalfor coupling the output nodeto the input terminal of the external isolation switch.

9 FIG. 8 FIG. 8 9 FIGS.and 900 900 800 is a schematic representation of alternative example switching driver circuitryincluding three half-bridges. The alternative switching driver circuitryis similar to, and includes many features in common with, the switching driver circuitryof. Such common features are denoted by common reference numerals inand will not be described again here for the sake of clarity and brevity.

900 800 840 436 430 852 850 8 FIG. The alternative switching driver circuitrydiffers from the switching circuitryofin that it omits the coupling switch. Thus, the output nodeof the second half-bridgecan be coupled to the ground railby closing (i.e. switching on) the ground switch.

800 900 880 8 FIG. In a similar matter to the switching driver circuitryof, the alternative switching driver circuitryis operable in a first (high output power) mode, a second (lower output power) mode and a third (lowest output power) mode, based on the results of comparisons performed by the control circuitryof the level of the input signal SIn to first and second thresholds.

880 900 6 460 1 2 412 414 476 Thus, if the level of the input signal Sin is equal to or greater than the first threshold, the control circuitrymay cause the switching driver circuitryto operate in its first mode by outputting a suitable control signal Cto switch off the isolation switchand outputting suitable control signals C, Cto control the first high-side switchand the first low-side switchto generate the required output voltage VOut across the load.

880 900 6 460 3 4 9 432 434 850 476 If the level of the input signal SIn is lower than the first threshold, but equal to or greater than the second threshold, the control circuitrymay may cause the switching driver circuitryto operate in its second mode, by outputting a suitable control signal Cto switch on the isolation switch, and outputting suitable control signals C, C, Cto control the second high-side switch, the second low-side switchand the ground switchto generate the required output voltage VOut across the load.

880 900 6 460 7 8 9 832 834 850 476 If the level of the input signal SIn is lower than the second threshold, the control circuitrymay may cause the switching driver circuitryto operate in its third mode, by outputting a suitable control signal Cto switch on the isolation switch, and outputting suitable control signals C, C, Cto control the third high-side switch, the third low-side switchand the ground switchto generate the required output voltage VOut across the load.

880 6 460 9 850 1 2 3 4 7 8 412 414 432 434 832 834 412 414 432 434 460 832 834 850 416 410 476 If the level of the input signal is zero (or less than a third threshold that is lower than the second threshold), the control circuitrymay output a suitable control signal Cto switch on the isolation switch, and may output suitable control signals Cto switch on the ground switch, and may output suitable control signals C, C, C, C, C, Cto switch off the first high-side switch, the first low-side switch, the second high-side switch, the second low-side switch, the third high-side switchand the third low-side switch. With the switches,,,,,,,in this configuration, the output nodeof the first half-bridgeis coupled to ground, such that no output voltage VOut develops across the load.

8 9 FIGS.and 6 FIG. 7 FIG. 1 2 3 2 3 1 In the examples shown in, first, second and third supply voltages +/−VSup, +/−VSupand +/−VSupare required. It will be appreciated by those of ordinarily skill in the art that the second and third supply voltages +/−VSup, +/−VSupcould be generated from the first supply voltage +/−VSupusing two instances of LDO circuitry of the kind described above with reference to, or using two instances of charge pump circuitry of the kind described above with reference to. More generally, in implementations that use more than two half-bridges and thus require a plurality of additional supply voltages, the plurality of additional supply voltages can be generated from the first supply voltage using a plurality of LDOs or a plurality of charge pumps, or a combination of one or more LDOs and one or more charge pumps.

4 5 8 9 FIGS.,,and In many applications it is beneficial to use single-ended output stages of the kind described above with reference toto minimise the number of switches required to implement the half-bridges, and to minimise the number of external capacitors and inductors required for low-pass filtering. However, in some applications it may be more beneficial to use a bridge-tied load configuration for the output stage.

10 FIG. is a schematic representation of switching driver circuitry according to the present disclosure that uses a bridge-tied load (BTL) configuration.

1000 1000 1010 1012 1014 1022 1 1024 1016 1012 1014 1000 1030 1000 1016 1010 1030 10 FIG. 10 FIG. The switching driver circuitry, shown generally atin, implements a Class D amplifier output stage. The switching driver circuitrycomprises a first high-power half-bridge, comprising a first high-side switchand a first low-side switchcoupled in series between a first positive power supply railthat receives a first positive power supply voltage +VSupfrom a power supply (not shown) and a first ground power supply railthat receives a first ground (i.e. 0V) power supply voltage GND from the power supply. An output nodeof the first high-power half-bridge between the first high-side switchand the first low-side switchis coupled, in use of the switching driver circuitry, to a first input terminal of a load, which may be, for example, an audio output transducer such as a speaker. It will be appreciated that a practical implementation the switching driver circuitrymay include first output low-pass LC filter circuitry between the output nodeof the first high-power half-bridgeand the first input terminal of the load. Such filter circuitry is not shown infor the sake of clarity.

1000 1040 1042 1044 1022 1024 1046 1040 1042 1044 1000 1030 1000 1046 1040 1030 1010 1040 1050 1080 10 FIG. The switching driver circuitryfurther comprises a second high-power half-bridge, comprising a second high-side switchand a second low-side switchcoupled in series between the first positive power supply railand the first ground power supply rail. An output nodeof the second high-power half-bridgebetween the second high-side switchand the second low-side switchis coupled, in use of the switching driver circuitry, to a second input terminal of the load. Again, it will be appreciated that a practical implementation the switching driver circuitrymay include second output low-pass LC filter circuitry between the output nodeof the second high-power half-bridgeand the second input terminal of the load. Such filter circuitry is not shown infor the sake of clarity. In switching driver circuitry having such output low-pass LC filter circuitry, it will be understood that compensation circuitry may also be included to compensate for mismatch between the first and second output low-pass LC filter circuitry of the BTL configuration, such that when transitioning between different output stages (i.e. different pairs of half-bridges,,,), transient effects at the output such as pops and clicks are eliminated.

1010 1040 1 1012 1014 1042 1044 1012 1014 1042 1044 1012 1014 1042 1044 2 3 The first and second high-power half-bridges,are configured to switch relatively high voltages. For example, the magnitude of the first positive power supply voltage VSupmay be of the order of 60 volts or more. The first high-side switch, the first low-side switch, the second high-side switchand the second low-side switchare capable of supporting such relatively high voltages. The first high-side switch, the first low-side switch, the second high-side switchand the second low-side switchmay be, for example, wide bandgap devices or high electron mobility transistor (HEMT) devices based on, for example, Gallium Nitride (GaN), Silicon Carbide (SiC), Gallium Oxide (Ga0) or other semiconductor materials. In a particular example, the first high-side switch, the first low-side switch, the second high-side switchand the second low-side switchare GaN switches.

1000 1050 1052 1054 1062 2 1064 1056 1050 1052 1054 1072 1072 1016 1010 The switching driver circuitryfurther comprises a first low-power half-bridge, comprising a third high-side switchand a third low-side switchcoupled in series between a second positive power supply railthat receives a second positive power supply voltage +VSupand a second ground power supply railthat receives a ground (i.e. 0V) power supply voltage GND. An output nodeof the first low-power half-bridgebetween the third high-side switchand the third low-side switchis coupled to an input terminal of a first isolation switch. An output terminal of the first isolation switchis coupled to the output nodeof the first high-power half-bridge.

1000 1080 1082 1084 1062 1064 1086 1080 1082 1084 1074 1074 1046 1040 The switching driver circuitryfurther comprises a second low-power half-bridge, comprising a fourth high-side switchand a fourth low-side switchcoupled in series between the second positive power supply railand the second ground power supply rail. An output nodeof the second low-power half-bridgebetween the fourth high-side switchand the fourth low-side switchis coupled to an input terminal of a second isolation switch. An output terminal of the second isolation switchis coupled to the output nodeof the second high-power half-bridge.

1050 1080 1010 1040 2 1052 1054 1082 1084 The first and second low-power half-bridges,are configured to switch lower voltages than the first and second high-power half-bridges,. For example, the magnitude of the second power supply voltage VSupmay be of the order of 12 volts or less. The third high-side switch, the third low-side switch, the fourth high-side switchand the fourth low-side switchare capable of supporting such voltages and may be implemented, for example, using silicon-based MOSFETs.

1072 1050 1010 1052 1054 1050 1050 1072 1022 1072 1010 1050 1072 1072 1012 1014 1010 1012 1014 1010 1072 2 3 The first isolation switchis operable to isolate the first low-power half-bridgefrom the first high-power half-bridge, such that the first supply voltage VSup (which could damage the switches,of the first low-power half-bridge) are not transmitted to the first low-power half-bridge. The first isolation switchis capable of supporting relatively high voltages of the kind supplied by the first positive supply rail. In particular, the first isolation switchis configured such that, when switched off, such relatively high voltages cannot pass from the first high-power half-bridgeto the first low-power half-bridge. The first isolation switchmay be, for example, a wide bandgap device or a high electron mobility transistor (HEMT) device based on, for example, Gallium Nitride (GaN), Silicon Carbide (SiC), Gallium Oxide (Ga0) or other semiconductor materials. The first isolation switchneed not be of the same type as the switches,of the first high-power half-bridge. For example, the switches,of the first high-power half-bridgemay be GaN switches, and the first isolation switchmay be a SiC switch.

1074 1080 1040 1082 1084 1080 1080 1074 1022 1074 1040 1080 1074 1074 1082 1084 1080 1082 1084 1080 1074 2 3 Similarly, the second isolation switchis operable to isolate the second low-power half-bridgefrom the second high-power half-bridge, such that the first supply voltage VSup (which could damage the switches,of the second low-power half-bridge) are not transmitted to the second low-power half-bridge. The second isolation switchis capable of supporting relatively high voltages of the kind supplied by the first positive supply rail. In particular, the second isolation switchis configured such that, when switched off, such relatively high voltages cannot pass from the second high-power half-bridgeto the second low-power half-bridge. The second isolation switchmay be, for example, a wide bandgap device or a high electron mobility transistor (HEMT) device based on, for example, Gallium Nitride (GaN), Silicon Carbide (SIC), Gallium Oxide (Ga0) or other semiconductor materials. The second isolation switchneed not be of the same type as the switches,of the second high-power half-bridge. For example, the switches,of the second high-power half-bridgemay be GaN switches, and the second isolation switchmay be a SiC switch.

1000 1090 1000 1090 1000 The switching driver circuitryfurther comprises control circuitry(which may also be referred to as modulator circuitry) configured to control the operation of the switching driver circuitrybased on an input signal Sin, received by the control circuitry, that represents a signal to be amplified by the switching driver circuitry.

1000 1 2 1090 1012 1014 3 4 1090 1042 1044 5 6 1090 1052 1054 7 8 1090 1082 1084 9 10 1072 1074 In use of the switching driver circuitry, control signals C, Care supplied by the control circuitryto control terminals of the first high-side switchand the first low-side switch, respectively, to control operation of those switches. Similarly, control signals C, Care supplied by the control circuitryto control terminals of the second high-side switchand the second low-side switch, respectively, to control operation of those switches, while control signals C, Care output by the control circuitryto control terminals of the third high-side switchand the third low-side switch, respectively, control signals C, Care output by the control circuitryto control terminals of the fourth high-side switchand the fourth low-side switch, respectively, and control signals C, Care output to control terminals of the first and second isolation switches,, respectively, to control operation of those switches.

1000 1072 1074 1010 1040 1 1 1030 9 10 1072 1074 1072 1074 1050 1010 1080 1040 The switching driver circuitryis operable in a first (high-power output) mode in which the first and second isolation switches,are open (switched off) and the first and second high-power half-bridges,supply either +VSup, −VSupor 0V to the load. In the first mode, the control signals Cand Care supplied, respectively, to the first and second isolation switches,to turn the first and second isolation switches,off, thus decoupling and isolating the first low-power half-bridgefrom the first high-power half-bridge, and decoupling and isolating the second low-power half-bridgefrom the second high-power half-bridge.

1 2 3 4 1090 1012 1044 1014 1042 1042 1014 1012 1044 1012 1042 1014 1044 1012 1042 1014 1044 1014 1044 1012 1042 The control signals C, C, C, Coutput by the control circuitryin the first mode are arranged such that either i) the first high-side switchand the second low-side switchare switched on at the same time (with the first low-side switchand the second high-side switchbeing switched off), or ii) the second high-side switchand the first low-side switchare switched on at the same time (with the first high-side switchand the second low-side switchbeing switched off), or iii) the first and second high-side switches,and the first and second low-side switches,are all switched off, or iv) the first high-side switchand the second high-side switchare switched on at the same time (with the first low-side switchand the second low-side switchbeing switched off); or v) the first low-side switchand the second low-side switchare switched on at the same time (with the first high-side switchand the second high-side switchbeing switched off).

1030 1010 1040 1 1012 1044 1 1042 1014 1012 1042 1014 1044 1012 1042 1014 1044 1014 1044 1012 1042 Thus, in the first mode, the output voltage VOut supplied across the loadby the combination of the first and second high-power half-bridges,may take one of three values: i) +VSup(when the first high-side switchand the second low-side switchare switched on), ii) −VSup(when the second high-side switchand the first low-side switchare switched on), and iii) 0V (when the first and second high-side switches,and the first and second low-side switches,are all switched off, or when the first and second high-side switches,are switched on and the first and second low-side switches,are switched off, or when the first and second low-side switches,are switched on and the first and second high-side switches,are switched off).

5 6 7 8 1052 1054 1082 1084 1052 1054 1082 1084 In the first output mode, the control signals C, C, C, Csupplied to the third high-side switch, the third low-side switch, the fourth high-side switchand the fourth low-side switch, respectively, may cause the third high-side switch, the third low-side switch, the fourth high-side switchand the fourth low-side switchto be held open (i.e. switched off).

1000 1072 1074 9 10 1050 1080 2 2 1030 The switching driver circuitryis also operable in a second (low-power output mode), in which the first and second isolation switches,are closed (i.e. switched on) in response to suitable control signals C, C, and the combination of the first and second low-power half-bridges,supplies either +VSup, −VSup, or 0V to the load.

9 10 1072 1074 1072 1074 1056 1050 1030 1086 1080 1030 In the second, low-power output mode, the control signals C, Care supplied to the first and second isolation switches,, respectively, to turn the first and second isolation switches,on, thus coupling the output nodeof the first low-power half-bridgeto the first terminal of the loadand coupling the output nodeof the second low-power half-bridgeto the second terminal of the load.

5 6 7 8 1090 1052 1084 1054 1082 1082 1054 1052 1084 1052 1082 1054 1084 1052 1082 1054 1084 1054 1084 1052 1082 The control signals C, C, C, Coutput by the control circuitryin the second, low-power output mode are arranged such that either i) the third high-side switchand the fourth low-side switchare switched on at a time (with the third low-side switchand the fourth high-side switchbeing switched off), or ii) the fourth high-side switchand the third low-side switchare switched on at a time (with the third high-side switchand the fourth low-side switchbeing switched off), or iii) the third and fourth high side switches,and the third and fourth low-side switches,are all switched off, or iv) the third high-side switchand the fourth high-side switchare switched on at the same time (with the third low-side switchand the fourth low-side switchbeing switched off); or v) the third low-side switchand the fourth low-side switchare switched on at the same time (with the third high-side switchand the fourth high-side switchbeing switched off).

1030 1050 1080 2 1052 1084 2 1082 1054 1052 1082 1054 1084 1052 1082 1054 1084 1054 1084 1052 1082 1 2 3 4 1012 1014 1042 1044 1012 1014 1042 1044 Thus, in the second, low-power output mode, the output voltage VOut supplied across the loadby the combination of the first and second low-power half-bridges,may take one of three values: i) +VSup(when the third high-side switchand the fourth low-side switchare switched on), ii) −VSup(when the fourth high-side switchand the third low-side switchare switched on), and 0V (when the third and fourth high side switches,and the third and fourth low-side switches,are all switched off, or when the third and fourth high-side switches,are switched on and the third and fourth low-side switches,are switched off, or when the third and fourth low-side switches,are switched on and the third and fourth high-side switches,are switched off). In the second mode, the control signals C, C, C, Csupplied to the first high-side switch, the first low-side switch, the second high-side switchand the second low-side switch, respectively, may cause the first high-side switch, the first low-side switch, the second high-side switchand the second low-side switchto be held open (i.e. switched off).

1090 1000 1090 1090 1000 The control circuitryis configured to control the mode of operation of the switching driver circuitrybased on a level (e.g. a magnitude or envelope) of the input signal SIn received by the control circuitry. The control circuitrymay be configured to compare the level if the input signal SIn to a first threshold and, based on the result of this comparison, cause the switching driver circuitryto operate in either its first (high-power output) mode or its second (low-power output) mode.

1030 2 1030 1050 1080 For example, if the level of the input signal Sin is equal to or greater than the first threshold, this may be indicative that an output voltage VOut across the loadof a magnitude greater than that of the second supply voltage VSupis required for the loadto generate an output signal of a desired magnitude (e.g. an audio output of a desired volume) and thus cannot be supplied by the combination of the first and second low-power half-bridges,.

1090 1000 9 10 1072 1074 1 2 3 4 1012 1014 1042 1044 1030 Thus, if the level of the input signal Sin is equal to or greater than the first threshold, the control circuitrymay cause the switching driver circuitryto operate in its first (high-power output) mode, by outputting suitable control signals C, Cto switch off the first and second isolation switches,and outputting suitable control signals C, C, C, Cto control the first high-side switch, the first low-side switch, the second high-side switchand the second low-side switchto generate the required output voltage VOut across the load.

1030 1030 2 1050 1080 In contrast, if the level of the input signal SIn is lower than the first threshold, this may be indicative that the magnitude of the output voltage VOut across the loadrequired for the loadto generate an output signal of a desired magnitude (e.g. an audio output of a desired volume) is less than (or equal to) that of the second supply voltage VSupand can thus be supplied by the combination of the first and second low-power half-bridges,.

1090 1000 9 10 1072 1074 5 6 7 8 1052 1044 1082 1084 1030 Thus, if the level of the input signal is less than the first threshold, the control circuitrymay cause the switching driver circuitryto operate in its second (low-power output) mode, by outputting suitable control signals C, Cto switch on the first and second isolation switches,, and outputting suitable control signals C, C, C, Cto control the third high-side switch, the third low-side switch, the fourth high-side switchand the fourth low-side switchto generate the required output voltage VOut across the load.

1000 1030 If the level of the input signal is zero (or less than a second threshold that is lower than the first threshold), this may be indicative that no output signal is required, such that the switching driver circuitrycan operate in a quiescent mode in which no output voltage VOut is supplied to the load.

1000 9 10 1072 1074 1 4 1012 1014 1042 1044 1010 1040 5 8 1052 1054 1082 1084 1050 1080 1012 1014 1042 1044 1052 1054 1082 1084 1016 1046 1010 1040 1030 Thus, if the level of the input signal is zero (or less than the second threshold), the control circuitrymay output suitable control signals C, Cto switch on the first and second isolation switches,and may output suitable control signals C-Cto switch off the switches,,,of the first and second high-power half-bridges,and may also output suitable control signals C-Cto switch off the switches,,,of the first and second low-power half-bridges,. With the switches,,,,,,,in this configuration, the output nodes,of the first and second high-power half-bridges,are at ground potential, such that no output voltage VOut develops across the load.

1000 9 10 1072 1074 1 4 1012 1042 1014 1044 1012 1042 1014 1044 1030 Alternatively, the control circuitrymay output suitable control signals C, Cto switch on the first and second isolation switches,and may output suitable control signals C-Cto either: i) switch the first and second high-side switches,on and switch the first and second low-side switches,off, or ii) switch the first and second high-side switches,off and switch the first and second low-side switches,on. In either of these switch configurations, the differential voltage across the loadis 0V.

1000 1000 1030 1 9 1012 1014 1042 1044 1052 1054 1082 1084 10 FIG. By selecting between the first (high-power output) mode and the second (low-power output) mode based on the level of the input signal SIn, the switching driver circuitryofis capable of efficiently supplying a highly accurate output voltage over a wide range. In particular, operating the Class D amplifier circuitryin its second (low-power output) mode when the level of the input signal Sin is less than the first threshold (and in the quiescent mode when the input signal level is zero or less than the second threshold) and in its first (high-power output mode) when the level of the input signal SIn is equal to or greater than the first threshold ensures that there is minimal unnecessary headroom in the supply voltage that is switched to provide the output voltage VOut to the load, while also enabling highly accurate control of the magnitude of the output voltage without requiring excessively low duty cycles for the control signals C-Cthat control the switches,,,,,,,.

1050 1080 It will be appreciated by those of ordinary skill in the art that it may be beneficial to ensure that the output voltage VOut has fallen to a level that can be tolerated by the switches of the third and fourth half-bridges,before switching from the first (high-power output) mode and the second (low-power output) mode.

1000 1092 1094 1092 1016 1010 1 1050 1072 1090 1016 1010 1 Thus, the switching driver circuitrymay further comprise first comparator circuitryand second comparator circuitry. The first comparator circuitryis configured to compare the voltage at the output nodeof the first high-power half-bridgeto a first low-power output mode threshold VLPM(indicative of an output voltage level that can be tolerated by the switches of the first low-power half-bridge), and to prevent the first isolation switchfrom being switched on (e.g. by outputting an appropriate first comparator output signal to the control circuitry) unless or until the voltage at the output nodeof the first high-power half-bridgehas fallen below the first low-power output mode threshold VLPM.

1094 1046 1040 2 1080 1 1074 1090 1046 1040 2 Similarly, the second comparator circuitryis configured to compare the voltage at the output nodeof the second high-power half-bridgeto a second low-power output mode threshold VLPM(indicative of an output voltage level that can be tolerated by the switches of the second low-power half-bridge, which may be equal to the first low-power output mode threshold VLPM), and to prevent the second isolation switchfrom being switched on (e.g. by outputting an appropriate second comparator output signal to the control circuitry) unless or until the voltage at the output nodeof the second high-power half-bridgehas fallen below the second low-power output mode threshold VLPM.

1050 1080 1090 1092 1094 1010 1040 1072 1074 1052 1054 1082 1084 1050 1080 1090 1056 1050 1072 1086 1080 1074 1090 1012 1014 1042 1044 1010 1040 In some examples, the first and second low-power half-bridges,, the control circuitryand, optionally, the first and second comparator circuitry,may be provided on a single IC, while the first and second high-power half-bridges,and the first and second isolation switches,are external to the IC. In such examples, the control terminals of switches,,,of the first and second low-power half-bridges,may be coupled, internally of the IC, to appropriate outputs of the control circuitry, and the IC may be provided with a first half-bridge output terminal for coupling the output nodeof the first low-power half-bridgeto the input terminal of the first external isolation switch, a second half-bridge output terminal for coupling the output nodeof the second high-power half-bridgeto the input terminal of the second external isolation switch, and with control output terminals for coupling outputs of the control circuitryto control terminals of switches,,,of the external first and second high-power half-bridges,.

1050 1080 1090 1092 1094 1090 1010 1040 1072 1074 1052 1054 1082 1084 1050 1080 1090 1056 1050 1072 1086 1080 1074 1090 1012 1014 1042 1044 1010 1040 In other examples, t the first and second low-power half-bridges,, the control circuitryand, optionally, the first and second comparator circuitry,may be provided on a single IC, but the control circuitrymay be external to the IC, as well as the first and second high-power half-bridges,and the first and second isolation switches,. In such examples, the IC is provided with input terminals for receiving control signals for the switches,,,of the first and second low-power half-bridges,from the external control circuitry, and with first half-bridge output terminal for coupling the output nodeof the first low-power half-bridgeto the input terminal of the first external isolation switch, a second half-bridge output terminal for coupling the output nodeof the second high-power half-bridgeto the input terminal of the second external isolation switch, and with control output terminals for coupling outputs of the control circuitryto control terminals of switches,,,of the external first and second high-power half-bridges,.

11 FIG. is a schematic representation of alternative example switching driver circuitry according to the present disclosure, which includes circuitry for generating a second supply voltage form a first supply voltage.

1100 400 11 FIG. 4 FIG. 4 11 FIGS.and The alternative switching driver circuitry, shown generally atin, includes a number of features in common with the switching driver circuitryof. Such common features are denoted by common reference numerals inand will not be described again here, for the sake of clarity and brevity.

1100 400 430 1110 1120 1100 432 1110 2 1110 1120 1120 434 2 1120 4 FIG. The switching driver circuitrydiffers from the switching driver circuitryofin that the second half-bridgeis coupled between first and second reservoir capacitors,. A first (positive) terminal of the first reservoir capacitoris coupled to an input terminal of the second high-side switchand a second terminal of the first reservoir capacitoris coupled to ground, such that a second positive supply voltage +VSupcan be supplied by the first terminal of the first reservoir capacitor. A first (positive) terminal of the second reservoir capacitoris coupled to ground, and a second terminal of the second reservoir capacitoris coupled to an output terminal of the second low-side switch, such that a second negative supply voltage −VSupcan be supplied by the second terminal of the second reservoir capacitor.

1110 1120 2 472 1 1100 The first and second reservoir capacitors,can be charged up to the second positive and negative supply voltages +/−VSup, respectively, by using the inductorto store energy from the first supply voltage +/−VSupin a charging mode of operation of the switching driver circuitry.

1120 2 1100 To charge the second reservoir capacitorto the second negative supply voltage −VSup, the switching driver circuitryoperates in a plurality of cycles, each cycle comprising a first phase and a second phase.

412 414 460 1 2 6 480 422 472 476 478 472 In the first phase, the first high-side switchis switched on and the first low-side switchand the isolation switchare switched off (in response to suitable control signals C, C, Coutput by the control circuitry), causing current to flow from the first positive power supply railthrough the inductorand loadto the ground rail, storing energy in the inductor.

412 414 432 1 2 3 480 460 434 6 4 480 1120 472 476 2 In the second phase, the first high-side switch, the first low-side switchand the second high-side switchare switched off (in response to suitable control signals C, C, Coutput by the control circuitry), and the isolation switchand the second low-side switchare switched on (in response to suitable control signals C, Coutput by the control circuitry). In this second phase, current flows from the second reservoir capacitorthough the inductorand load, causing the voltage −VSupto become more negative.

The voltage drop VL across the inductor at the start and end of a cycle of operation is equal to 0. It can be shown that:

412 where D is a duty cycle of the first high-side switch.

2 412 1 Thus, the second negative supply voltage −VSupis a function of the duty cycle of the first high-side switch, the first positive supply voltage +VSupand the output voltage VOut.

1110 2 1100 Similarly, to charge the first reservoir capacitorto the second positive supply voltage +VSup, the switching driver circuitryoperates in a plurality of cycles, each cycle comprising a first phase and a second phase.

414 412 460 1 2 6 480 424 472 476 478 472 In the first phase, the first low-side switchis switched on and the first high-side switchand the isolation switchare switched off (in response to suitable control signals C, C, Coutput by the control circuitry), causing current to flow from the first negative power supply railthrough the inductorand loadto the ground rail, storing energy in the inductor.

412 414 434 1 2 3 480 460 432 6 3 480 472 1110 2 In the second phase, the first high-side switch, the first low-side switchand the second low-side switchare switched off (in response to suitable control signals C, C, Coutput by the control circuitry), and the isolation switchand the second high-side switchare switched on (in response to suitable control signals C, Coutput by the control circuitry). In this second phase, current flows from the inductorto the first reservoir capacitor, causing the voltage +VSupto become more positive.

It can be shown that:

414 where D is a duty cycle of the first low-side switch.

2 414 1 Thus, the second positive supply voltage +VSupis a function of the duty cycle of the first low-side switch, the first negative supply voltage −VSupand the output voltage VOut.

4 5 8 11 FIGS.,, and- In the examples illustrated in, the high-side switches are shown as being implemented using PMOS devices (or equivalent wide bandgap devices or high electron mobility transistor (HEMT) devices based on, for example, Gallium Nitride (GaN), Silicon Carbide (SiC), Gallium Oxide (Ga203) or other semiconductor materials, for the half-bridges that switch the highest supply voltages). In alternative examples, the high-side switches may instead be implemented as using NMOS devices (or equivalent wide bandgap devices or high electron mobility transistor (HEMT) devices based on, for example, Gallium Nitride (GaN), Silicon Carbide (SIC), Gallium Oxide (Ga203) or other semiconductor materials, for the half-bridges that switch the highest supply voltages), with suitable adaptation of the control signals output by the control circuitry.

2 480 2 4 5 8 11 FIGS.,and- The magnitude of the second supply voltage VSupmay be determined based on a based on a level (e.g. a magnitude or envelope or volume) of the input signal Sin received by the control circuitry, and thus the magnitude of the second supply voltage VSupmay vary dynamically in operation of the switching driver circuitry described above with reference to.

4 5 8 11 FIGS.,and- 10 FIG. In the example switching driver circuitry described above with reference to, when the switching driver circuitry changes from one operating mode to another, using a different half-bridge (or pair of half-bridges, in BTL arrangements of the kind shown in) to switch a different supply voltage, the control (modulator) circuitry that controls the switches of the half-bridges should adapt the duty cycles of the switches according to the supply voltage to be switched in the new operating mode, to prevent the occurrence of artefacts (e.g. audible pops or clicks) in an output of the load.

12 FIG. 4 5 8 11 FIGS.,and- is a schematic representation of an example digital modulator suitable for use as the control circuitry of the switching driver circuitry described above with reference to.

12 FIG. 4 5 8 11 FIGS.,and- 1210 1200 1220 1230 1240 1250 1252 1254 1210 1210 In, an amplifierrepresents switching driver circuitry of the kind described above described above with reference to. The modulator, shown generally at, includes a loop filter, a divider, and a quantisercoupled in a forward pathbetween an input nodeat which an input signal SIn is received and an output nodecoupled to the switching driver circuitryto supply a modulated output signal SOut to the switching driver circuitry.

1260 1270 1254 1280 1220 A feedback pathincluding a multipliercouples the output nodeto a first input of a subtractor, which is configured to subtract a scaled version of the output signal SOut from the input signal SIn. The result of this subtraction is input to the loop filter.

1240 1200 1240 1240 The quantisermay be a linear quantiser, in which case the modulatoris a sigma-delta modulator and is followed by a pulse width modulation (PWM) modulator (not shown) coupled to the output of the quantiser to convert sigma-delta codes output by the quantiserinto PWM pulses. Alternatively, the quantisermay be a PWM quantiser.

1270 1260 1210 1210 400 1 1 1200 1210 1200 4 FIG. The multiplierin the feedback pathis configured to multiply the output signal SOut by a digital signal PVDD* representing the supply voltage PVDD currently being switched by the half-bridge(s) that are active in the current operating mode of the switching driver circuitry. For example, if the switching driver circuitryis switching driver circuitryof the kind described above with reference toand is currently operating in its first (high-power output) mode of operation, PVDD is equal to VSup, such that PVDD* is a digital signal representative of VSup. The digital signal PVDD* may be supplied by an analog to digital converter (ADC) coupled to a supply rail of the currently active half-bridge, or may be supplied by a host system incorporating the modulatorand switching driver circuitry. This multiplication ensures that the modulatorsupplies controls signals having the correct duty cycle for the current supply voltage PVDD.

1230 1200 1230 The dividerin the forward path is configured to (at least approximately) divide the signal in the forward path by the signal PVDD*, to maintain a noise transfer function (NTF) and loop behaviour of the modulatorwithin acceptable limits. The dividermay be implemented using a look-up table, for example.

1270 1270 1230 1250 1210 The arrangement of the multiplierin the feedback pathand the dividerin the forward pathensures that as PVDD changes (when the switching driver circuitrychanges between operating modes to use different supply voltages) the correct duty cycle is used to control the switches of the half-bridge(s) that is (are) active, and thus prevent the occurrence of artefacts (e.g. audible pops or clicks) in an output signal output by the load.

The circuitry described above with reference to the accompanying drawings may be incorporated in a host device such as a laptop, notebook, netbook or tablet computer, a gaming device such as a games console or a controller for a games console, a virtual reality (VR) or augmented reality (AR) device, a mobile telephone, a portable audio player or some other portable device, or may be incorporated in an accessory device for use with a laptop, notebook, netbook or tablet computer, a gaming device, a VR or AR device, a mobile telephone, a portable audio player or other portable device.

The skilled person will recognise that some aspects of the above-described apparatus and methods may be embodied as processor control code, for example on a non-volatile carrier medium such as a disk, CD- or DVD-ROM, programmed memory such as read only memory (Firmware), or on a data carrier such as an optical or electrical signal carrier. For many applications embodiments of the invention will be implemented on a DSP (Digital Signal Processor), ASIC (Application Specific Integrated Circuit) or FPGA (Field Programmable Gate Array). Thus the code may comprise conventional program code or microcode or, for example code for setting up or controlling an ASIC or FPGA. The code may also comprise code for dynamically configuring re-configurable apparatus such as re-programmable logic gate arrays. Similarly the code may comprise code for a hardware description language such as Verilog TM or VHDL (Very high speed integrated circuit Hardware Description Language). As the skilled person will appreciate, the code may be distributed between a plurality of coupled components in communication with one another. Where appropriate, the embodiments may also be implemented using code running on a field-(re) programmable analogue array or similar device in order to configure analogue hardware.

Note that as used herein the term module shall be used to refer to a functional unit or block which may be implemented at least partly by dedicated hardware components such as custom defined circuitry and/or at least partly be implemented by one or more software processors or appropriate code running on a suitable general purpose processor or the like. A module may itself comprise other modules or functional units. A module may be provided by multiple components or sub-modules which need not be co-located and could be provided on different integrated circuits and/or running on different processors.

As used herein, when two or more elements are referred to as “coupled” to one another, such term indicates that such two or more elements are in electronic communication or mechanical communication, as applicable, whether connected indirectly or directly, with or without intervening elements.

This disclosure encompasses all changes, substitutions, variations, alterations, and modifications to the example embodiments herein that a person having ordinary skill in the art would comprehend. Similarly, where appropriate, the appended claims encompass all changes, substitutions, variations, alterations, and modifications to the example embodiments herein that a person having ordinary skill in the art would comprehend. Moreover, reference in the appended claims to an apparatus or system or a component of an apparatus or system being adapted to, arranged to, capable of, configured to, enabled to, operable to, or operative to perform a particular function encompasses that apparatus, system, or component, whether or not it or that particular function is activated, turned on, or unlocked, as long as that apparatus, system, or component is so adapted, arranged, capable, configured, enabled, operable, or operative. Accordingly, modifications, additions, or omissions may be made to the systems, apparatuses, and methods described herein without departing from the scope of the disclosure. For example, the components of the systems and apparatuses may be integrated or separated. Moreover, the operations of the systems and apparatuses disclosed herein may be performed by more, fewer, or other components and the methods described may include more, fewer, or other steps. Additionally, steps may be performed in any suitable order. As used in this document, “each” refers to each member of a set or each member of a subset of a set.

Although exemplary embodiments are illustrated in the figures and described below, the principles of the present disclosure may be implemented using any number of techniques, whether currently known or not. The present disclosure should in no way be limited to the exemplary implementations and techniques illustrated in the drawings and described above.

Unless otherwise specifically noted, articles depicted in the drawings are not necessarily drawn to scale.

All examples and conditional language recited herein are intended for pedagogical objects to aid the reader in understanding the disclosure and the concepts contributed by the inventor to furthering the art, and are construed as being without limitation to such specifically recited examples and conditions. Although embodiments of the present disclosure have been described in detail, it should be understood that various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the disclosure.

Although specific advantages have been enumerated above, various embodiments may include some, none, or all of the enumerated advantages. Additionally, other technical advantages may become readily apparent to one of ordinary skill in the art after review of the foregoing figures and description.

It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. The word “comprising” does not exclude the presence of elements or steps other than those listed in a claim, “a” or “an” does not exclude a plurality, and a single feature or other unit may fulfil the functions of several units recited in the claims. Any reference numerals or labels in the claims shall not be construed so as to limit their scope.